TIM 58 Chapter 6, continued: Behavioral Modeling

Sample Sequence Diagram

Building Sequence Diagrams Set the context Identify actors and objects that interact in the use-case scenario Set the lifeline for each object Add messages by drawing arrows Shows how they are passed from one object to another Include any parameters in parentheses Obvious return values are excluded Add execution occurrence to each object’s lifeline Validate the sequence diagram Ensures that it depicts all of the steps in the process

Communication Diagrams Depict the dependencies among the objects An object diagram that shows message passing relationships Emphasize the flow through a set of objects

Communication Diagram Syntax

Sample Communication Diagram

Building Communication Diagrams Set the context Identify objects, actors and associations between them Lay out the diagram Add the messages Validate the model

Behavioral State Machines Objects may change state in response to an event Different states are captured in this model Shows the different states through which a single object passes during its life May include the object’s responses and actions Example: patient states New patient—has not yet been seen Current patient—is now receiving treatment Former patient—no longer being seen or treated Typically used only for complex objects

Components of State Machines States—values of an object’s attributes at a point in time Events—the cause of the change in values of the object’s attributes Transitions—movement of an object from one state to another May include a guard condition to flag that a condition is true and allow the transition

State Machine Syntax

Sample State Machine An event is something that takes place at a certain point in time and changes value(s) that describe an object. This in turn causes a change in the state of the object. Examples of events include a condition becoming true, a receipt of a call fro a method by an object, and the passage of a designated period of time. An action is an atomic, non-decomposable process that cannot be interrupted. Actions are often modeled as if they are completed in zero time, and they are associated with a transition. An activity is a non-atomic, decomposable process that can be interrupted. Activities take a long period of time to complete, they can be started or stopped by actions, and they are associated with states.

Guidelines for Creating Behavioral State Machines Use only for complex objects Draw the initial state in the upper left corner Draw the final state in the bottom right corner Use simple, but descriptive names for states Look out for “black holes” and “miracles” Ensure guard conditions are mutually exclusive Ensure transitions are associated with messages and operations In the parlance of behavioral state machines, every event leads to a state transition. This is because events are defined as anything that changes a value which in turn describes the state of the behavioral state machine. In other words, transitions occur only as the result of an event. Specific types of events are as follows.   a) Data value change: a change in one of the data values that collectively describe the state of the object. For example, a patient transitions from “new” to “existing” after the first visit. b) Boolean condition: a Boolean test that is applied at a certain point. For instance, after a patient transitions to “existing” we may ask the question “is the patient insured?” which would lead to state changes based on billing policies. c) Time lapse: after a certain amount of time in a given state, the object may spontaneously change to a different state. For instance, a patient that is in state “inactive” (perhaps because he/she has no future appointments), may be removed from the system after 5 years.

Building a Behavioral State Machine Set the context Identify the states of the object Initial Final Stable states during its lifetime Lay out the diagram—use a left to right sequence Add the transitions Identify the triggers (events that cause the transition) Identify the actions which execute Identify the guard conditions Validate the model—ensure all states are reachable

CRUDE Analysis Helps to identify object collaborations Labels object interaction in 5 possible ways: Create—can one object create another? Read—can one object read the attributes of another? Update—can one object change values in another? Delete—can one object delete another object? Execute—can one object execute the operations of another? Utilizes a matrix to represent objects and their interactions Most useful as a system-wide representation

Sample CRUDE Matrix

Verifying & Validating Behavioral Models Actors must be consistent between models Messages on sequence diagrams must match associations on communication diagrams Every message on a sequence diagram must appear on an association in a communication diagram Guard conditions on a sequence diagram must appear on a communication diagram Sequence of messages must correspond to the top down ordering of messages being sent State transitions must be associated with a message on a sequence diagram Entries in a CRUDE matrix imply messages being sent all transitions contained in a behavior state machine must be associated with a message being sent on a sequence and communication diagram, and it must be classified as a (C)reate, (U)pdate, or (D)elete message in a CRUDE matrix

Summary Behavioral Models—provide a detailed view of how object collaborations support use-cases Interaction Diagrams Sequence diagrams Communication diagrams Behavioral State Machines—depicts the states of complex objects during its lifetime CRUDE Analysis—helps to identify potential collaborations Verifying & Validating behavioral models—ensures the completeness and consistency of the models